Many conduit installations are subjected to sizeable temperature and pressure variations, and for this reason it is frequently necessary to provide pipes, ducts and the like with one or more expansion joints to accommodate the pipe growth, shrinkage or displacement.
One approach to solving the problem of providing compensation for separative thrust at expansion joints is exemplified in my own earlier U.S. Pat. No. 4,018,463, issued Apr. 19, 1977. In that patent, the compensating portions are all encased in a large outside cylindrical portion having a maximum diameter appreciably larger than the pipe diameters which the coupling is intended to join. Large annular members are also provided within the cylindrical portion. Articulating connections are attached to the annular members within the space enclosed by the cylindrical portion, and cannot be accessed for repair or replacement without first entirely disassembling the pipe joint by removal of the cylindrical member.
In my U.S. patent application Ser. No. 6,439, a different approach to thrust compensation for expansion pipe joint couplings is taken. In that application, the compensating members are located entirely outside of the expansion pipe joint. This greatly simplifies the construction, and renders much simpler the task of repair or replacement of various components of the joint. Prior art pertinent generally to this particular approach includes U.S. Pat. No. 2,545,701, McCausland, issued Mar. 20, 1951, and U.S. Pat. No. 3,458,219, Wesch, issued July 29, 1969.
In McCausland, there is provided a bellows-like expansion joint, together with a plurality of exteriorly mounted thrust compensating devices, one of which includes a cylinder connected to one pipe end and a piston within the cylinder connected to the other pipe end. The volume within the cylinder on one side of the piston is adapted to be pressurized with the fluid contained in the pipes themselves, and this pressure seeks to cause relative movement between the piston and the cylinder which would compensate for the separative thrust on the expansion joint.
In the Wesch patent, the compensation is brought about by way of tension coiled springs connected between flanges attached to the pipe ends, and a telescoping cylindrical member is provided between the pipe ends to allow the expansion itself to take place.
My earlier U.S. patent application Ser. No. 6,439 had as one of its aims to provide a thrust-compensating expansion joint for pipe ends, in which articulation of one pipe end with respect to the other, as well as axial displacement of the one with respect to the other, is permitted over a relatively large range.
A further aim of that application was to provide a cylinder/piston thrust-compensating assembly for an expansion pipe joint, in which the cylinder was not subjected to axial stress, as occurs in the prior art.
In my subsequent continuation-in-part U.S. patent application Ser. No. 345,063, a principal aim was to provide a cylinder/piston thrust-compensating assembly for an expansion pipe joint, in which the cylinder is not located radially adjacent the expansion assembly, so that removal thereof to gain access to the expansion assembly itself is facilitated.
In two of the embodiments in continuation-in-part U.S. patent application Ser. No. 345,063, the expansion joint included, between the two pipe ends, a hollow cylinder with a cylindrical outer surface, two ring members having an inner cylindrical surface for engagement with one end of the outside surface of the hollow cylinder, and having male spherical surface means on the outside, for engagement with female spherical surfaces provided on or firmly attached to the respective pipe end.
In the designs of the two embodiments just mentioned, there was provision for maintaining the ring members in hydraulic balance, so that no axial force was applied against the ring members. This minimizes wear of the seating surfaces and reduces the risk of binding. The present invention encompasses these two embodiments, and adds a third, in which the structure is markedly simpler than the first two.